1. Field of the Invention
This invention relates to an ink jet print head having a construction in which a head chip and a circuit substrate are interconnected by a flexible print substrate through an anisotropic conductor film, for use in a recording unit and in an ink jet type recording apparatus, for example. More particularly, the invention relates to a molding structure of an interconnecting portion that prevents corrosion and disconnection of an anisotropic conductor film (hereinafter called ACF) at the interconnecting portion resulting from exposure of the AFC to ink and ink vapor during a continuous printing operation, at the time of a maintenance of a recording apparatus, during production of a head and during storage under a packaged state for a long time, and that eliminates discharge defects.
2. Description of the Related Art
Various ink jet printer heads having a construction in which a head chip and a circuit substrate are interconnceted by a flexible print subtrate (hereinafter called “FPC subtrate”) through an anisotropic conductor file have been marketed in recent years.
FIG. 3 shows a construction of a heretofore known ink jet print head. As shown in FIG. 3, the ink jet print head includes as its main components a nozzle plate 40, a nozzle support plate 30, a head chip 50, an aluminum base 20, a flow passage substrate 60, a circuit substrate 10 for supplying electrical signals to drive the head chip 50 and an FPC substrate for interconnecting the circuit substrate to the head chip, not shown in FIG. 3.
Ink droplets jetted from the head chip shoot onto a print paper or print medium through fine apertures formed on the nozzle plate. The fine ink droplets that fail to shoot but change to mist tend to float and adhere to the nozzle plate surface and to the head outer peripheral portion. Dust in the air and the ink droplets remaining at the time of ink suction also adhere to the nozzle plate suface. Therefore, when continuous printing is make, the operation must be conducted while the nozzle surface is preiodcally wiped by use of a wiper blade to remove a large number of fine floating ink droplets, dusts and residual ink droplets adhering to the nozzle plate surface. Continuous printing in a normal printing operation is achieved while such maintenance is conducted.
The known ink jet print head has a construction shown in FIG. 2. This drawing is a sectional view of the known ink jet print head taken along a line A–A′ of the ink jet head shown in FIG. 3. The drawing shows the section of a structural portion for interconnecting the head chip 50 including the circuit substrate 10 and the piezoelectric ceramic plate by the FPC substrate 70 through the ACF 80.
As shown in the drawing, the ACF 80 is molded with an adhesive 110 lest it comes into direct contact with external air. This structure is a single-layered molding structure sealed by a sealant such as an epoxy adhesive, a silicone adhesive or an acrylic adhesive. A sealant having low permeability of air and vapor is used for the sealant, and protects the interconnecting portion from changes of temperature and humidity. When oil ink, water base ink, solvent ink or UV-curing ink is used as ink, however, it becomes difficult to secure sufficient sealing performance and corrosion resistance, and such functions have been required and proposed (refer, for example, to Japanese Patent No. 2,904, 629 (p 9 –11, FIG. 1)).
A two-layered molding structure has also been proposed as a method of improving sealing performance of a seal portion that interconnects the head chip 50 to the flow passage substrate 60, though this seal portion is different from the seal portion of the invention (refer, for example, to Japanese Patent No. 3,117,340).
When continuous printing is conducted for a long time at a high printing ratio that consumes large amounts of oil ink, water base ink, solvent or UV-curing ink within a short preiod, a problem develops in that residual ink that cannot be removed sufficiently by the wiping operation described above invades gaps among head constituent components. This problem results for capillary acting on the gaps between the constituent compoents and on the gaps with a casing for fitting the head. Due to capillary action, ink finally reaches the bonding portion of the FPC substrate of the head, corrodes and disconnects the ACF and invites discharge defects. Moisture-proofing means alone is not sufficient.
When ink is accidentally dropped and is caused to adhere to the bonding portion of the FPC substrate during production of the head or during maintenance of the recording apparatus having the head fitted thereto, the problem described above similarly occurs if ink is left standing as such for a long time.
Since the head is put into a plastic bag and is preserved under the sealed state at the time of packaging and shipment while a certain amount of ink remains, it is allowed to stand for a long time under an atomosphere of an extremely high ink concentration. Therefore, ink vapor enters the bonding portion of the FPC substrate of the head, corrodes and disconnects the ACF and invites the discharge defect.
In view of the problems described above, the invention aims at providing an ink jet print head that prevents corrosion and disconnection of the AFC by ink, ink vapor and moisture in air, and eliminates the discharge defect by molding the bonding portion of the FPC substrate of the ink jet head as a whole by use of a sealant.